We demonstrate a single-sideband in-fiber frequency shifter using acousto-optic polarization mode coupling. Using 200 mW power to a bulk shear-wave acoustic transducer bonded to a polarization-preserving D-fiber, we have observed power coupling from an optical carrier to an upper sideband, shifted by the 17.5 MHz acoustic frequency. The suppression of the lower sideband, relative to the upper sideband level is at least 10 dB, with the actual sideband level below the noise level of the experiment. This frequency shifting property may be used for the development of in-fiber Bragg cells with improvement of the weak 0.16% observed power coupling efficiency in this work.
We describe a new fabrication technology for silica-based integrated optical components that employs electron irradiation to modify the refractive index of an amorphous SiO2 substrate. An asymmetric planar waveguide has been fabricated with this method, with a guide depth of approximately 5 micrometers and a core-cladding index difference on the order of 10-3. The guide is single-moded over the entire visible spectrum, exhibiting losses of less than 12 dB/cm.
We present a theoretical investigation of the dispersive properties of linearly-chirped fiber Bragg gratings, establishing optimal parameters for the refractive index variation along the fiber length. Employing numerical methods, we show that a 3-cm-long chirped Bragg filter is able to compensate for the dispersion from 100 km of fiber at 1.2 micrometers , recompressing a 20 os Gaussian input pulse from its dispersion-broadened 74.4 ps width back to 20.6 ps. We also prove that a uniform grating profile provides the optimum compression for this input pulse type, confirming recently published claims.
KEYWORDS: Optical filters, Single mode fibers, Acoustics, Electronic filtering, Polishing, Signal detection, Signal attenuation, Wave propagation, Polarization, Step index fibers
Since its initial demonstration by Kim and Blake[1,2]. the in-fiber frequency shifter has seen several modifications including cascaded acoustic interactions,[3] new acoustic horn designs,[4] new acoustic coupling geometries,[5] and novel mode filters, [6] This device employs elliptical-core two-mode fiber, i.e., fiber which supports the LP01 and the LP11 modes.
All-fiber acousto-optic modulators have been proposed for applications in which large insertion losses or back- reflections due to fiber-air or fiber-integrated optic interfaces cause detrimental effects.[1] Many sensing applications, such as the fiber-optic gyroscope and other heterodyned interferometers have such a requirement. A component of great interest in these applications is the in-fiber frequency shifter.
The state of polarization of light propagating in a polarization-preserving fiber may be varied via the acousto-optic effect by introducing high-frequency acoustic waves into the core region of the fiber. This effect may provide active polarization control for applications in interferometry, switching, and amplitude modulation. This paper describes a method for inducing polarization coupling within an optical fiber by coupling bulk shear acoustic waves through the flat surface of an elliptical-core D-fiber. The theory of device operation is developed, and a device model is characterized. The effect is experimentally verified with a first-generation device achieving approximately 7% amplitude coupling efficiency at 2 W input electrical power at a frequency of 22.7 MHz.
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